In modern projection exposure apparatuses for microlithography for the production of extremely small structures in the field of electrical engineering or micromechanics, such as, in particular, EUV (extreme ultraviolet) projection exposure apparatuses which are operated with extreme ultraviolet light, optical elements which have to be positioned correspondingly exactly are desirable. In particular, it may be desirable to alter the position of the corresponding optical elements, such that actuators have to be provided which enable the changes in position of the optical elements such as, in particular, of mirrors in EUV projection exposure apparatuses. Such projection exposure apparatuses including actuators for changing the position of optical elements are described in DE 102006 038455 A1, WO 2008/122313 A1, DE 102005 057860 A1, DE 60126103 T2, DE 10339362 A1, DE 10140608 A1, DE 10053899 A1, WO 2008/012336 A1, EP 1503246 A2, EP 1720068 A1, U.S. Pat. No. 7,046,335 B2, EP 1321823 A2, WO 2007/010011 A2.
On account of the size and weight of the optical elements to be positioned, it may be desirable to use gravitation compensators which compensate for the weight force of the corresponding optical elements, such that, during the movement of the optical elements, the actuators do not simultaneously have to bear the entire supporting load. As a result, the actuation of the optical elements by the actuators is simplified and a lower energy input into the actuators is desirable. This in turn has positive effects on the overall behavior of the projection exposure apparatus, since, by way of example, no additional thermal loads are introduced into the apparatus on account of the high energy consumption of the actuators. Such gravitation compensators are described e.g. in EP 1475669 A1 and WO 2009/093907 A1. Furthermore, magnetic bearing devices are known from DE 69825747 T2, US 2004/0212794 A1, WO 2006/087463 A1, JP 55060719 A and JP 58137618 A.
However, the movement of the optical elements as a result of the actuation of the actuators has the effect that the gravitation compensators also enable a corresponding movement. Particularly in the case of large and heavy optical elements such as, for example, corresponding mirrors in EUV projection exposure apparatuses, this can lead to problems, however, on account of the high compensation forces or compensation loads.
In previous gravitation compensators it has been ascertained, in particular, that the positioning accuracy of the optical elements can be impaired when gravitation compensators are used, and that the positioning accuracy can be disadvantageously influenced particularly in specific atmospheres that are used in EUV projection exposure apparatuses, such as hydrogen-containing atmospheres. The positioning stability over a relatively long period of time can also be adversely affected.